Controller area network (CAN) systems are currently being implemented as common networking systems for automotive and industrial applications. In a typical automotive application, the CAN provides a two (or one) wire link that can be routed around the entire vehicle. This link may illustratively be terminated by 120 ohm loads at each end. A CAN provides a lightweight and cost effective means for the vehicle's central processing unit to communicate with satellite peripheral modules, e.g., dome lamps, door modules, headlight modules, taillight modules, anti-skid braking system (ABS) modules, airbag modules, etc. The CAN wire itself is specified by the International Standards Organization (ISO) for at least a ten meter length. Unfortunately, this long wire acts as an ideal antenna that can be subject to automotive-type transients, as well as industrial-type transients, such as electromagnetic interference (EMI) and electrostatic discharge (ESD).
In order to operate in the harsh environments of automotive and industrial settings, a CAN transceiver must successfully withstand these high voltage transients and must be capable of handling the standard automotive requirements of double battery and 40 volt load dump. It must also withstand shorts from the CAN wire to V.sub.cc, ground and V.sub.bat, and any other power supply associated with the system. These requirements are typically specified as the ability to survive voltages on the CAN wire(s) between +40 and -6 volts.
A controller area network (CAN) transceiver in accordance with the prior art is shown in FIG. 1. It consists of a CAN-H driver and a CAN-L driver. CAN-H uses a pnp (or a PMOS) transistor as an active device, while CAN-L uses an npn (or an NMOS) transistor as an active device. In order to obtain high speed and symmetry, it is desirable to use low voltage, matched components. However, in this configuration, these low voltage components cannot withstand high voltage conditions due to gate oxide integrity issues and drain-to-source breakdown voltage limitations. High voltage components are not desirable for CAN applications due to their larger gate capacitances, and hence their slower operation. These high voltage components also incur a considerable silicon area penalty.
In a differential CAN driver of the types described in relation to the prior art and the present invention, there is a need to match the impedances of the two legs during switching and during the dominant state, and to match the timing of the two switching devices.